Major ocean currents such as the Loop Current in the eastern Gulf of Mexico have surface manifestations which can be exploited for remote sensing. Surface chlorophyll-a concentrations, which contribute to the shift in color from blue to green in the open sea, were found to have high spatial variability; significantly lower concentrations were observed in the current. The cyclonic edge of the current is an accumulation zone which causes a peak in chlorophyll concentration. The dynamics also cause surface concentrations of algae, which have a high reflectance in the near infrared. Combining these observations gives rise to an edge effect which can show up as a bright lineation on multispectral imagery delimiting the current's boundary under certain environmental conditions. When high seas introduce bubbles, white caps, and foam, the reflectance is dominated by scattering rather than absorption. This has been detected in ERTS imagery and used for current location

Maul, G. A.

English

NASA Technical Reports Server

P 
Paper M 13 
REMOTE SENSING OF OCEAN CURRENTS USING ERTS IMAGERY 
George A. Mau I, National Oceanic and Atmospheric Administration, Atlantic 
Oceanographic and Meteorological Laboratories, Miami, Florida 
ABSTRACT 
Major ocean cur ren ts  such as the  Loop 
Current i n  t h e  eas t e rn  Gulf of Mexico have 
sur face  manifestat ions which can be ex- 
p l o i t e d  f o r  remote sensing.  A time s e r i e s  
t o  study c e r t a i n  aspec ts  of the  sur face  
expression of t h i s  cu r ren t  was begun i n  
August 1 9 7 2 .  Surface chlorophyl l -a  con- 
cen t r a t ions ,  which cont r ibu te  t o  the  s h i f t  
i n  c o l o r  from blue t o  green i n  the. open 
sea ,  were found t o  have high s p a t i a l  v a r i a -  
b i l i t y ;  s i g n i f i c a n t l y  lower concentrat ions 
were observed i n  the  cur ren t .  The cyclonic  
edge of the cur ren t  i s  an accumulation zone 
which causes a peak i n  chlorophyll  concen- 
t r a t i o n .  The dynamics a l s o  cause sur face  
concentrat ions of a lgae ,  which have a high 
r e f l ec t ance  i n  the  near  i n f r a red .  Com- 
bining these  observations gives r i s e  t o  an 
"edge e f f e c t "  which can show up as a 
br igh t  l i n e a t i o n  on mul t i spec t r a l  imagery 
de l imi t ing  the  c u r r e n t ' s  boundary under 
c e r t a i n  environmental condi t ions.  Frequent- 
l y  the  s e a - s t a t e  i n  the  cur ren t  i s  higher 
than i n  surrounding water due t o  d i f f e ren -  
t i a l  shear .  When high seas  introduce 
bubbles, white caps, and foam, the r e f l e c -  
tance i s  dominated by s c a t t e r i n g  r a t h e r  
than absorpt ion.  This has been detected 
i n  ERTS imagery and used f o r  cur ren t  
loca t ion .  
~ r l ~ l n ~ l  photography may be eurchcmd 
EROS Data Center 1365 
p ~ a r n I N G  PAGE BLANK NOT F 
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1 
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INTRODUCTION 
The major circulation feature of the Gulf of Mexico is 
the so-called Loop Current. This flow enters the basin as 
a well formed western-boundary current through the Yucatan 
Straits. It penetrates into the Gulf to a varying lati- 
tude before it exits through the Straits of Florida. 
Transporting vast amounts of heat, salt and momentum, the 
current significantly affects circulation on the shdlf, 
local fisheries, marine trans ortation, and is thought to 
The current boundary separates two water masses . Across 
the boundary there is a difference in temperature, sal- 
inity, color, velocity, and biomass. These surface 
manifestations can be used for remote sensing in our 
efforts to monitor the current's variability. However, 
surface temperature difference, one of the best indicators, 
is not usable in the subtropics due to summer insolation 
which makes the sea surface isothermal. Other surface 
features, such as ocean color and evidences of horizontal 
current shear, probably have less seasonal variability, 
This paper is a pre1,iminary report on a time series of 
observations across the surface boundary layer of the 
Loop Current, and its detection by remote sensing, using 
several aspects of the surface features. The research 
is designed to investigate the seasonal variability of the 
juxtaposed water masses, both temporally and spatially, 
and the detection by ERTS of their boundary. 
be associated with hurricane P ntensification. 
FIELD EXPERIMENTS 
The field work began in June 1972 with a ship/aircraft 
experiment designed to detect the color boundary of the 
Loop Current front south of Dry Tortugas. The NASA C-130 
flew over the research vessel track which was oriented in 
the same azimuth as ERTS suborbital track. Seven 
altitudes were flown, at 100 mb decrements, over the ship. 
Aircraft data collection included RC-8 color and color IR 
photography as well as multispectral photography to sim- 
ulate the ERTS MSS imagery, PRT-5 sea surface temperature 
profiles, Bendix 24 channel scanner data, and inflight re- 
cordings of atmospheric temperature, pressure and 
moisture . 
Prior to the aircraft overflights the scientific crew 
aboard RIV BELLOWS located the boundary. Measurements of 
1366 
ocean temperature, chlorophyll-a, volume scattering 
function, and salinity were made every ten meters down 
to 50 meters; Fore1 color, and upwelling-and downwelling 
spectral irradiance were taken at each of the five 
stations that bracketed the front. During the over- 
flights on the following day, closely spaced surface 
measurements of the same variables (except irradiance) 
were taken. All measurements were made using standard 
oceanographic techniques or analyzed by methods detailed 
by Strickland and Parsons (1968). 
In August 1972 a time series of the Loop Current by ship 
and satellite was begun. The cruise plan is to occupy 
the suborbital track of ERTS that crosses the west 
Florida shelf approximately 200 kilometers west of 
Tampa and terminates in the center of the Yucatan 
Straits. Every 36 days, the R/V VIRGINIA KEY is on the 
suborbital track. Continuous surface observations of 
radiometric temperature (in conjunction with the NOAA-2 
IR sensors) and chlorophyll-a (by the fluorometric 
method of Lorenzen, 1966) are made; at approximately 12 
kilometer intervals XBT's are taken, and samples are 
drawn for salinity, bulk temperature, volume scattering 
function, and biomass analysis. At appropriate daylight 
stations, measurements of upwelling and downwelling 
spectral radiance are made using a 1/4 meter Ebert scan- 
- ning spectro-radiometer. A standard hydrographic sec- 
tion of the Yucatan Straits is made in order to estimate 
the geostrophic transport relative to 800 db. After the 
section, the cyclonic edge of the current is tracked by 
following the pathline of the 22'  C isotherm at 100 
meters; this pathline loops from the western edge of 
Yucatan to the Florida Straits south of Dry Tortugas 
and is in close proximity to the surface front. Finally 
another hydrographic section is observed along the sub- 
orbital track of ERTS that passes from Key West to 
Havana. 
It is planned to continue the cruises to collect one 
year of data in order to obtain an evalutaion of the 
seasonal variability. The final field experiment, 
planned for the autumn, is a SKYLAB/EREP mission in- 
volving a ship and an aircraft. 
PRELIMINARY RESULTS 
The cyclonic edge of the Loop Current tends to concen- 
trate flotsam and jetsam. Natural materials, such as 
surface marine algae, were seen from the June photo- 
1367 
graphy t o  have a p i n k i s h  cast on c o l o r  I R  (SO 397) f i l m ;  
t h i s  i s  confirmed i n  black and white I R  photography ( type 
2424 f i l m  and a 89B Wratten F i l t e r ) .  When these  a l g a e  
are p resen t ,  they  appear as a b r i g h t  l i n e a t i o n  marking 
t h e  edge o f  t h e  c u r r e n t  i n  ERTS MSS-6 (0.7-0.8um). 
A second consequence of  t h e  boundary l a y e r  dynamics is t o  
concent ra te  ch lorophyl l  bear ing  organisms. A t y p i c a l  
p r o f i l e  ac ross  t h e  c u r r e n t  boundary i s  given i n  f i g u r e  1. 
This t r a n s e c t  i s  from Key West harbor ,  ou t  t h e  channel 
i n t o  t h e  c o a s t a l  water, and ac ross  t h e  f r o n t .  The fea- 
t u r e  of  i n t e r e s t  i s  t h e  peak i n  ch lorophyl l -a  concen- 
t r a t i o n  j u s t  a t  t h e  boundary. This i s  a phenomenon 
no t i ced  i n  each of  t h e  s i x  c r u i s e s  t o  d a t e  and occurs  
to a varying degree i n  t h e  deep s e a  as w e l l  as near  shore. 
D e t a i l s  o f  t h e  v a r i a b i l i t y  w i l l  have t o  await f u r t h e r  
sampling because of expected seasonal  and b i o l o g i c a l  
dependence. 
towards t h e  green would occur and enhance t h e  boundary i n  
MSS-4(0.5-0.6pm). This does indeed happen a s  w i l l  be 
d iscussed  below. 
One would expect however t h a t  a s h i f t  
A t h i r d  observa t ion  i s  t h e  usua l  change i n  s e a  s t a t e  
ac ross  t h e  boundary. When winds and a s s o c i a t e d  waves 
c r o s s  i n t o  zones of  high c u r r e n t  v e l o c i t y  wi th  an 
opposing s e t ,  t h e  seas gene ra l ly  b u i l d  up r ap id ly .  I t  
i s  n o t  uncommon f o r  t h e  s e a  s t a t e  t o  inc rease  from 1 
t o  2 meters when c ross ing  i n t o  t h e  c u r r e n t .  Thus an 
inc rease  o f  white  caps,  foam, and bubbles i s  encountered 
nea r  t h e  edge which inc reases  t h e  r e f l e c t a n c e  i n  t h e  
c u r r e n t .  This r a i s e s  t h e  r e f l e c t a n c e  i n  a l l  channels ,  
bu t  i n  a non-uniform (wavelength dependent) manner. 
The term "edge effect" (Maul, 1972) was coined t o  des-  
c r i b e  these  phenomena which can be e x p l Q i t e d  t o  d e t e c t  
Other s t reaming 
events ,  such as sediments being en t r a ined  by t h e  Gulf 
Stream af te r  pass ing  source reg ions  such as Cape 
Hatteras (ERTS 1132-1509-2), can be considered p a r t  o f  
t h i s  edge effect .  I t  a l lows a m u l t i s p e c t r a l  approach 
t o  recognize t h e  boundary of t hese  c u r r e n t s  i n  t h e  
absence o f  sea su r face  temperature changes. 
To understand t h e  phys ics  of r e f l e c t i o n  from t h e  ocean, 
cons ider  a simple model of  an ocean o f  s e m i - i n f i n i t e  
depth ( Z )  wi th  s p h e r i c a l  s c a t t e r i n g .  The s p e c t r a l  
r e f l e c t a n c e  R(2,-)  i s  def ined  a s  t h e  r a t i o  of  t h e  
' t h e  boundary of  major ocean c u r r e n t s .  
1368 
upwelling irradiance H(z,+), i.e. that from the ocean, 
to the downwelling irradiance H(Z,-), i.e. that from the 
sky and sun: 
The reflectance is tacitly assumed to be a function of 
wavelength. From scattering theory the reflectance at 
the sea surface (Z=O) can be shown to be 
R(0,-) =: l - H ( p ) K  
where uo is the ratio of the scattering coefficient (b) 
to the attenuation coefficient (d ,  H(p) is the so- 
called H-function for various scattering albedos (uo) as 
tabulated by Chandrasekhar (1960) and p is the cosine of 
the zenith angle. It should be emphasized that this model 
does not include multiple scattering or the angular 
dependence of scattering such as the Monte Carlo calculations 
of Gordon and Brown (1973). Nevertheless it provides an 
analytic solution to the radiative transfer equation which 
illustrates the fundamental variables in reflectance. 
An example of calculated reflectance from a plane water 
surface with the sun in the zenith [H(po)] is given in 
- figure 2 .  The curves are based on scattering and atten- 
uation coefficients given by Jerlov (1968) for natural 
ocean water bodies; a and b are chosen to exemplify the 
behavior of reflectance. Curve 1 is the spectral re- 
flectance for pure water. Curve 2 is generated by 
changing the attenuation coefficient due to an increased 
absorption coefficient (a=a-b) due to yellow substance. 
Note that the reflectance is lower and that the peak has 
shifted to a longer wavelength. Curve 3 is generated by 
increasing the scattering coefficient due to isotropic 
scatters whose b is twenty times the Rayleigh (molecu- 
1ar)scattering at 450  nm.; only the magnitude of the 
scattering increases, in a wavelength dependent-manner, 
with the peak invariant. Curve 4 combines the effects 
of absorption and scattering. The reflectance is lower 
than pure scattering and the wavelength of the peak is 
shifted to the green. 
Curves 1 and 4 can be likened to the change in reflec- 
tance encountered when crossing an ocean front. An 
example of an observed reflectance pair is taken from 
1369 
the June aircraft experiment and given in figure 3. 
These are uncorrected for the immersion effect and the 
reflectances are approximately 20% too high. The zenith 
angle was -20' in each case. H(Z,+) was measured 1 
meter below the surface. The Loop Current water (marked 
2) is lower in chlorophyll-a (< 0.1 mg m-3) and lower 
in volume scattering coefficient (B(45)=2.6~10'~m-') than 
the coastal water (marked 4) with 0.4 mg m-3 chlorophyll- 
a and fi(45)=5.4~10'~rn''. If one assumes that the ab- 
sorption coefficient is proportional to the chlorophyll- 
a concentration and the scattering coefficient is pro- 
portional to the volume scattering coefficient at 45O 
(Beardsley et al, 1970) then a qualitative confirmation 
of reflectancetheory is given. 
The curves further suggest that changes in ocean color 
will be reflected in MSS-4. Figures 4a and b are images 
from ERTS-1 taken over the eastern Gulf of Mexico dur- 
ing times of surface observations. Figure 4a is MSS-4 
'data showing the higher reflectance of water from Florida 
Bay pouring over the Keys and being entrained by the 
Gulf Stream. This image confirms the discussion in the 
previous paragraph. 
Figure 4b is MSS-5 data taken north of the Yucatan 
Straits during a period of surface observations. The 
curving discontinuity in the water masses outlines the 
edge of the current. However, the blue waters of the 
current are brighter than the adjoining waters in con- 
tradiction to the results in figure 3 .  The explanation 
must come from figure 2, where we see the effect of 
increased scatterers. A marked increase in sea state was 
encountered in the current, which can account for a much 
higher scattering coefficient due to entrapped air. 
An additional explanation of this is offered through con- 
sideration of sea state alpne. 
observed that with 15 m s- winds, 10% of the surface of 
the sea is covered with white caps, and white caps re- 
flect approximately 90%. 
is assumed to be 5 %  in the absence of white caps and 10% 
of the sea is covered with white caps, then reflectance 
is R=5%(.9) + 10%(.9)=13.5% or 270% higher than without 
white caps. 
The spectrum of total upwelling irradiance from above the 
Ocean HT(O,+) 3: [R(O,-') + Rs]H(O,-) where Rs is the 
Ross and Cardone (1972) 
If reflectance of the ocean 
1370 
reflectance of the surface (both diffuse and direct). 
For the case R - constant and a given H(0,-), HT depends 
on w,,. 
R ( 0 , - )  at 450 nm to that at 525 nm for pure water is a4 .5  
(curve 1). The same ratio with scatterers only in the 
water (curve 3) is 2.0. Quantitative confirmation with 
realistic scattering hase functions will 
T 
the signal of a differential radiometer (Arvesen, 1972) 
is subject to such variation in W O .  
that w,, always varies in the ocean such that R(O,-)s28 
is constant (Duntley, 1972), then a dual channel intru- 
ment will work in the absence of sea state changes. 
The solar spectrum is fairly flat in the visible region 
(H(0,-),,8,,/H(0,-) ,,".1.3). Hence, higher sea states, 
which reflect high percentages of white light, propor- 
tionally add more long wavelength energy to the upwell- 
ing irradiance. In terms of a chromaticity diagram, 
this means that the purity changes but not the dominant 
wavelength. To correct for sea state a channel in a 
multispectral scanner near 1 vm appears useful. At this 
wavelength there i s  a maximum in the attenuation coeffi- 
cient of pure water (i,e. w o + 6 ) ,  a maximum in atmospheric 
transmissivity, and the influence of chlorophyll seems 
low. 
From ffgure 2 we estimate that the ratio of 
calculated using the R onte Carlo code. 
If it is fortuitous 
CONCLUSIONS 
ERTS imagery has been successful in providing information 
on the ocean in both the nearshore and deep sea envir- 
onment. As the result of an edge effect the cyclonic 
side of the Gulf Stream can'reflect in several ERTS 
bands as a prominent feature paralleling the current's 
edge. It is lbund however that sea state is a signifi- 
cant variable that can dominate the reflectance and 
change the spectral signature of surface waters, The 
prospect is therefore raised that passive remote sensing 
using ERTS may be used to quantitatively estimate sea 
state and near surface winds in areas of homogeneous 
water masses. Further, the sea state problem must be 
considered a dominant variable in the determination of 
ocean color from aerospace sensors. 
1371 
REFERENCES 
Arvesen, J. C. (1972). Fourth Annual Earth Resources Re- 
view, Vol. IV, NASA MSC-05937, pp. 104-1 to 104-2. 
Beardsley, G. F., H. Pak, K. Carder, and B. Lundgren 
(1970). Journal of Geophysical Research, 75 (15), 
pp. 2 8 3 7 - 2 - 8 4 5 .  
Chandrasekhar, S. (1960). Radiative Transfer, Dover, 
New York, 393 pgs. 
Duntley, S. Q. (1972). Fourth Annual Earth Resources Re- 
Gordon, H. R. and 0. B, Brown (1973). Applied Optics. 
view, Vol. IV, NASA MSC-05937, pp. 102-1 t o  102-25. 
(in press). 
Jerlov, N. G. (1968). Optical Oceanography, Elsevier, 
New York, 194 pgs. 
Lorenzen, C. J. (1966). Deep Sea Research, 13, pp. 223- 
227. 
Maul, G, A,, (1972). Interim Report on Remote Sensing 
of Ocean Currents from ERTS, NASA-CR-12907, National 
Technical Information Center, E72-10233. 
Resources Review, Vol. IV, NASA MSC-05937, pp. 85-1 
Ross, D. B. and V. Cardone (1972). Fourth Annual Earth 
to 85-20. 
Strickland, J. D. H., and T. R, Parsons (1968). A Practi- 
cal Handbook of Seawater Analysis. Fisheries Re- 
search Board of Canada, Ottawa, 31'1 pgs. 
1372 
0 
I 
I 
0.5 
0.4 
0.3 
0.2 
0. I
0 I 
I 
I 
CI 
0 0 
30"- 
w 
5 
"5i 
280' 
29 ac w 
CL 
1E 
W 
1 
Figure 1: Surface temperature t r a c e  (upper) and surface 
chlorophyll-a p r o f i l e  (lower) across t h e  Loop Current f ron t  
and i n t o  Key West harbor. 
f i gu re  i s  approximately 75 kilometers. 
Horizontal s ca l e  across  t h e  
1373 
1374 
1375 


Remote sensing of ocean currents using ERTS imagery

The author has identified the following significant results. Fourteen field experiments in support of the NOAA investigation of ocean color boundary determination using ERTS-1 data have been conducted since June 1972. The boundary between coastal waters and the Loop Current has been detected by ERTS-1 as a result of sea state changes as well as color differences. Computer enchancement of MSS data are revealing many features not shown in the NDPF product. Analysis of the 24 channel MSS data shows that a thermal IR channel is required on an ERTS MSS to distinguish between atmospheric and sea state effects. Cloud cover analysis suggests the need for daily coverage of this type sensor for routinely useful oceanographic applications

"Aade' availablf under NASA sponsors ep
in the interest of early and wide dis- E 7. 4- 1 .02. '
semination of Earth Resources Survey =-/ 5
Program information and without liability
for any use made thereof."
REMOTE SENSING OF OCEAN CURRENTS
George A. Maul
National Oceanic and Atmospheric Administration
Atlantic Oceanographic and Meteorological Laboratories
15 Rickenbacker Causeway
Miami, Florida 33149
November 1973
Interim Report for Period May 1973 - November 1973
Prepared for:
GODDARD SPACE FLIGHT CENTER
Greenbelt, Maryland 20771
(E74-10025) REMOTE SENSING OF OCEAN N74-11160
CURRENTS Interim Report, Hay - Nov.
1973 (Naticnal Oceanic and Atmospheric
Administration) 10 p HC $3.00 CSCL 08C Unclas
G3/13 00025
https://ntrs.nasa.gov/search.jsp?R=19740003047 2020-03-23T14:04:34+00:00Z
TECHNICAL PORT STAJ.DARD TITLE PACE.Roport o. 
. Gavrnmn, Accession No. .kecp.n',s Cotaoag No.
. ogic. Clp n oat
4 November 1973
REMOTE SENSING OF OCEAN CURRENTS 6. Prloming; Orgono,.on Code
7.. uthor(s) George A. Maul a. Performing orgaonza on Rea,, N.
9. Performing Or;sniza°ion Name and Address 10. Work Unit No.
NOAA/AOML
15 Rickenbacker Causeway - It.nPct,0 iC .-
Mi ami, Florida 33149 13. Type of Report and Period Covered12. Sponsoring A;ency Name ond Address
-Interim Report.
* May 1973-November 1973
14. Sponsoring Agency Code
15. Supplemenory Notes
16. Abstract
Fourteen field experiments in support of the NOAA inyestigation- of-- --
ocean color boundary determination using ERTS data have.been+ con-
.ucted since June 1972. The boundary between.coastal waters and
the Loop Current has been detected by ERTS as a result of sea-state.. -
changes as weTl as color differences. Computer enhancement of MSS
data are reveal-ing many features not shown in the NDPF product.
Analysis of the 24 channel MSS data shows that a thermal IR channel
is required on an ERTS MSS to distinguish between atmospieric and'
-sea -state effects. Cloud cover analysis suggests the need for
daily coverage of this type sensor.for routinely useful oceanogra-
phic applications. -
* 
.
17. Key Words (S. trcted by Author(s)) 18. Distribution Statement
Detection of the color boundary
layer
iM. Security Classif. (of this i eport) .-j; Scurit Classi. (of this Pae) 21. No. f Pages 22. Price
UNCLASSIFIED UNCLASSIFIED
*For sae by the Clerinlouie for FeJera Scie:ific and Technical laorcioa. Spriagrfcld. Virsia. 22151.
Fure 2. Tec'- ical Report St ad-rd T;tle Pace
-S *'..- - -
Fiscal Report to accompany Type II Report for Period 5/4/73 - 11/4/73
ERTS Proposal No. 108
Ship Time:
June: $ 3000
July: 3400
August: 2800
September: 3000
Supplies: 5500
Travel: 900
Support: 2400
TOTAL $ 22000
PREFACE
The objective of this investigation is to locate ocean current boundaries
by sensing the color change associated with the cyclonic edge of the zone
of maximum horizontal velocity shear. The test site is the eastern Gulf
of Mexico where the strongly baroclinic flow from the Yucatan Straits
forms into the Loop Current. The research is using ERTS' data in the in-
vestigation of ocean color sensing.
A time series of the location of the Loop Current was begun in August
1972. For every other transit of ERTS (i.e., 36 days) the current is
located by ship. These data are being used to provide surface measure-
ments in support of the spacecraft observations and to obtain the first
time history of the circulation in the eastern Gulf of Mexico.
Further time histories'of the variables which allow the use of ocean
color as a current detection phenomenon are being-made. These research
cruises were conducted for over one year in order to understand the
seasonal variability associated with the circulation and detection of
the circulation's surface indicators.
INTRODUCTION
This interim report covers the third six months of the ocean current de-
tection project using ERTS data. Five field experiments have been con-
ducted in support of the work, all of which are part of a continuing time
history of the Loop Current. ERTS images which appear to show the current
boundary do so because of either changes in sea-state or ocean color.
FIELD DATA COLLECTION
Ship-satellite experiments were performed in June, July, August and
September. A time-series of the Loop Current was obtained by occupying
the suborbital track of ERTS that passes into the Yucatan Straits every
36 days. The research vessel was on the suborbital track on the day of
satellite transit collecting continuous chlorophyll-a, volume scattering,
and radiometric temperature (in conjunction with the NOAA-2 IR sensors);
hourly (15 km interval) expendable bathythermograph, surface bucket
temperature and salinity samples were obtained. During daylight, spectra.
of upwelling and downwelling radiance (400-800 nm) were measured with 1/4
meter Ebert scanning spectroradiometer, weather permitting. Upon reach-
ing the Yucatan Straits a temperature/salinity/depth (STD) transect of
nine stations were made in order to determine the geostrophic current and
transport fields. After the STD transect, the surface boundary of the
Loop Current was tracked using the same measurements outlined for the
subsatellite track. A second STD transect of the Florida Straits from
Key West to Havana was made in order to determine the discharge from the
basin.
AIRCRAFT EXPERIMENT
Continued study of the 24 channel Bendix MSS data across the Loop Current
fronthas shown that reflection patterns in the sea surface, presumably
caused by turbulent wind stress in the atmospheric boundary layer, are
seen at all but the longest (>8 m) infrared wavelengths. Physically
this is a statement that the longer wavelengths have higher emissivities
(and have lower reflectances), a well established fact. If these data
are extrapolated to spacecraft observations one would be unable to tell
if these shorter wavelength pattern observations were atmospheric (clouds,
fog, etc.) or oceanic. The long wavelength infrared observations can
resolve this question because if the patterns were atmospheric they would
appear in these data. Therefore, as a recommendation to future ERTS sen-
sors where water studies are to be made a 10.5-12.5 pm channel is required
to separate sea-state induced reflection patterns from thermally coupled
3
boundary regions, and indeed to add a degree-of-freedom to the analysis.
SHIP EXPERIMENT
The last cruise of the ERTS ground truth series was taken in September.
All in all, 15 cruises were made on the project, 3 were ship/aircraft
experiments, and 12 were the time-series of the Loop Current every 36
days from August 1972 to September 1973. The September 1973 cruise
report is attached; other reports for this six month period are attached
to the bimonthly reports.
Between August and September a large anticyclonic eddy detached from the
main current. The main flow was found at its lowest (latitude) since last
March and seems to confirm the hypothesis of an annual growth (spring)
eddy formation (summer) and collapse (fall-winter). The growth to the
northern Gulf coast was later this year than "usual" as remarked on by
the fishermen in that area noting that the larger animals did not come
until August this year (as compared to May, the "usual" period). This
was of course, caused by the flow patterns in the Loop Current.
Analysis of the ship data for transports through the straits, annual
chlorophyll-a variations, scattering and other optical property varia-
tions, and thermal variations will require a significant time block in
order to properly -correlate e hevariability to .be anticipated. Data
collection in the New York Bight as part of this laboratory's partici-
pation in MESA has begun. Those data will help to quantify our tentative
conclusions in the Bight and provide the ground truth for the time-series
being made in this area using ERTS data.
ERTS DATA
The results of many of the experiments using JPL's VICAR system have been
discussed in bimonthly reports and were presented as a paper at the
Annual Meeting of the ASP-ACSM, Orlando, Florida, in October 1973. The
paper is being written at this time for formal publication, however,
several computer experiments need to be done before the work is completed.
Many of these results were presented and discussed with personnel of
NOAA/NESS and the NASA ERTS review panel in late October 1973.
In summary, we found that most of the ocean information -is lost in the
NDPF product because the average scene radiance is half an order of
magnitude higher than the ocean scene. Computer enhancement brings out
features that are one DN different on the average, and these are the
levels across boundary layers in many cases. Several techniques such as
ratioing were tried but the straight enhancement by contrast stretching
seems to provide the most satisfactory results at this writing.
Several more important spectra have been obtained during a joint
NOAA-NASA ocean color experiment. These data include harbor water,
dredging sites, sewer-outfalls, and algae rich areas. Data processing
has begun to study ratios (etc.) with these data. This begins a cata-
loguing of spectra which hopefully will include a wide range of water
types and quality.
PROGRAM FOR NEXT REPORTING INTERVAL
Processing the physical, biological, and spectral data from the cruises
will consume the bulk of the next reporting period. Continued efforts
will be made with computer enhancement of selected scenes and with the
time-series in the New York Bight. Continued theoretical calculations
by H. R. Gordon (co-investigator) are being made concerning the nature
of photon transmission using the Monte Carlo code.
CONCLUSIONS
The time-series in the Gulf of Mexico has added significantly to our
understanding of the variabilityin this region. The current's
boundary is well correlated with local fisheries and a combination of
ship and satellite data is being used to explain the Florida east
coast red tide of November 1972. Computer processing is required to
extract current boundaries in the deep sea and is extremely important
in coastal areas. Analysis of 24 channel MSS data dictate the need
for a 11.5 pm infrared channel in a future ERTS for meaningful water
resources analysis.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
ATLANTIC OCEANOGRAPHIC AND METEOROLOGICAL LABORATORIES
PHYSICAL OCEANOGRAPHY LABORATORY
NASA/GSFC
CRUISE REPORT
R/V VIRGINIA KEY
17-23 September
1973
I. OBJECTIVES
The purpose of this cruise was to continue a time series of the
location of the Loop Current as part of AOML's project with the
Earth Resources Technology Satellite (ERTS) and the NOAA-2 Me-
teorological Satellite. The research is intended to obtain
baseline information on the spectroradiometric properties of
the ocean's surface useful for remote sensing and the detection
of that information at orbital altitudes.
II. SCHEDULE
Date Time Activity
September DST
17 0800 Depart Miami
18 1100 Commenced STD transect of Florida Straits
20 0000 Commence STD transect of Yucatan Straits
2000 Commence tracking current
21 1000 Satellite transit
22 0200 Complete survey
23 2200 Arrive Miami
III. STATION POSITIONS
The northern limit STD transect of the Florida Straits was at the
100-fathom curve south of Marquesa Key Light and terminated 12 n.
mi. north of Havana Cuba. The station locations were:
24021'N 82-09W Station 1
24011'N 82-11W 2
24005'N 82-16W 3
23055'N 82-19W 4
23044'N 82-23W 5
23034'N 82-28W 6
23021'N 82-29W 7
The station locations for the Yucatan Straits STD transect were:
21050'N 85-10'W 8
21048'N 85-20'W 9
21047'N 85-31'W 10
21045'N - - 85-40'W - -- - - 11 - -
21042'N 85-53'W 12
21 040'N 86-03'W 13
21038'N 86-12'W 14
21033'N 86-22'W 15
21031'N 86-33'W 16
The easternmost station was 12 n. mi. west of Cabo San Antonio the
westernmost station-was 12 n. mi. east of Isla Contoy.
The cruise from Isla Contoy to Dry Tortugas was a saw-toothed path,
which crossed the surface boundary layer zone of the current.
IV. PERSONNEL
Michael Ednoff, Chief Scientist FSU
John Hazelworth NOAA/AOML
Gary Dingle NOAA/AOML
V. DESCRIPTION OF OPERATIONS
Data collection commenced with an STD transect of the Florida Straits.
Continuous flow measurements of chlorophyll-a and continuous radio-
metric sea surface temperature were recorded on a dual channel re-
corder. While on the track, hourly XBTs, surface bucket temperature,
surface salinity, and measurements of scattering ratios were taken.
Spectra of upwelling and downwelling visible radiation were not ob-
served. Loran A fixes were made at one hour intervals and at major
course, and/or speed changes. One liter samples were filtered for a
7
spectrophotometer calibration of chlorophyll-a every six hours and
at major changes in the fluorescence, and for biological samples.
The final cruise of the time series observed that an anticyclonic
eddy detached between August and September. The eddy was confirmed
by a cruise of the R/V BOWERS just prior to the R/V VIRGINIA KEY's
cruise. The main current was found at its southernmost position
in six months and served to confirm the notion that an annual cycle
for the flow exists.
VI. LOGS
Chief Scientist Log
Deck Log
Track Chart
Loran Log (C&GS 722)
Hydrographic Station
Bathythermograph Log
Submitted by: George A. Maul
November 5, 1973


Remote sensing of ocean currents

There are no author-identified significant results in this report

"Made avaifable under NASA sponsorship .//
in the interest of early and wide dis-
semination of Earth Resofcires Sarvey 1. 1 .. 0 2 2
Program information and without liability (I'7 1 /3' , -
for any use made thereof."
Bimonthly Report: 1/4/73 to 3/4/73
ERTS Proposal No. 108
Remote Sensing of Ocean Currents
George A. Maul, Principal Investigator, GSFC ID-C0315
OBJECT
The object of this investigation is to locate ocean
current boundaries by sensing the color change associated
with the cyclonic edge of the zone of maximum horizontal
velocity shear. The test site is the eastern Gulf of
Mexico where the strongly baroclinic flow from the Yucatan
Straits forms into the Loop Current. The research will
attempt to use ERTS data in the investigation of ocean
color sensing from simultaneous observations by ship and
satellite.
FIELD DATA COLLECTION
A time-series of the Loop Current is being obtained by
occupying the suborbital track of ERTS that passes into the
Yucatan Straits every 36.days. The research vessel is on
the suborbital track on the day of satellite transit col-
lecting continuous chlorophyll-a and radiometric temperature(in conjunction with the NOAA-2 IR sensors); hourly (15 kmlinterval) expendable bathythermograph, volume scattering,
surface bucket temperature and salinity samples are being
obtained. During daylight, spectra of upwelling and down-
welling radiance (400-800 nm) are being measured with a 4
meter Ebert scanning spectroradiometer. Upon reaching the
Yucatan Straits a temperature/salinity/depth (STD) transect
of nine stations is being made in order to determine the
geostrophic current and transport fields. After the STD
transect, the surface boundary of the Loop Current is being
tracked using the same measurements outlined for the sub-
satellite track. A second STD transect of the Florida
Straits from Key West to Havana is made in order to deter-
mine the discharge from the basin.
WORK SUMMARY
Two cruises were undertaken during the reporting period.
Severe weather conditions limited the January cruise to the
transect line and several XBT transects to help define the
northern limit of the current. In February no STD stations
(URRENTS Bimj RtOTE SENSING OF OCEAN
CUNS nthlY Report, 4 Jan. -, N73-19
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.Amospheric Administrat oni . Jn - 4 CL 86/o N73-19330) .n
ton) 8 p C $3.00 UnclasCSCL 08J G3/13 00022
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https://ntrs.nasa.gov/search.jsp?R=19730010603 2020-03-23T03:22:24+00:00Z
-2-
were obtained due to instrument failure; the suborbital
trackline was shortened considerably because the cruises
are now based out of Miami instead of St. Petersburg. The
attached cruise reports detail the field trips.
The computer facilities at Patrick Air Force Base were
used for investigative analysis of ocean features of New
York Bight oriented ERTS data. Using the digital data the
effect of constrast stretching and range emphasis was made.
The dynamic range of ocean features is only about 5% of the
entire range present in a scene and must be greatly empha-
sized to ensure that all pertinent data are made available
for subsequent analyses. Initial analysis indicates that
there is subsequently more ocean information on a frame
than 'is ordinarily visible in the normally processed scene.
Programs have been written to use NOAA's Digital Muir-
head Display (DMD); the first successful run was accomplished
this week. In this run, a portion of the 16 August New York
Bight scene was contrast stretched to bring out what has
been interpreted by some as internal waves. The success has
been encouraging and scenes with lower signal to noise ratio
in the deep ocean will be studied.
A paper entitled, "Remote Sensing of Ocean Currents
Using ERTS Imagery", was presented at the ERTS Symposium in
Washington. Highlights of several topics discussed in
these reports were given. Theoretical calculations were
made that support the concern given in earlier reports of the
dominant effect of sea state on upwelling light. It was
further shown that sea state effects the spectrum in a wave-
length dependent manner making ratioing/differencing tech-
niques a three channel problem. The magnitude of the effect
is to be studied by an aircraft experiment described in the
last report.
WORK PLANS
The field work will continue in order to be on the
suborbital track for the 24 March and 29 April transits.
Routine processing of the cruise data will continue as
before.
The aircraft experiment discussed before is now planned
for the next reporting period. The lfight is weather
dependent; since this is an add-on study, it must be coor-
dinated with the NOAA PI and aircraft availability.
-3-
Image enhancement plans include experiments with
differentgamma functions and contrast stretching. Ratioing
and differencing will be started pending completion of
further-theoretical studies; initially these will be in the
form of profiles rather than whole images.
George A. Maul
NOAA/AOML-PhOL
15 Rickenbacker Causeway
Miami, Florida 33149
12 March 1973
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
ATLANTIC OCEANOGRAPHIC AND METEOROLOGICAL LABORATORY
PHYSICAL OCEANOGRAPHY LABORATORY
NASA/GSFC
CRUISE REPORT
M/V VENTURE
9-13 January 1973
I. OBJECTIVES
The purpose of this cruise was to continue a time series
of the location of the Loop Current as part of AOML's
project with the Earth Resources Technology Satellite
(ERTS) and the NOAA-2 Meteorological Satellite. The
research vessel steamed along the suborbital track of
ERTS that leads into the Yucatan Channel on the day of
satellite transit. The research is intended to obtain
baseline information on the spectroradiometric proper-
ties of the ocean's surface useful for remote sensing
and the detection of that information at orbital alti-
tudes.
II. ACTUAL SCHEDULE
Date Time Activity
January EST
9 1830 Departed Key West
11 1000 Satellite Transit
12 0030 Break off survey due to weather
13 1000 Arrive Key West
III. STATION POSITIONS
The suborbital track occupied had the following begin-
ning and ending coordinates:
27044'N 840 30'W
220 32'N 85034'W
i
-2-
IV. PERSONNEL
G. Maul, Chief Scientist NOAA/AOML
J. Hazelworth NOAA/AOML
R. Qualset NOAA/AOML
M. Ednoff FSU
--V.- -DESCRiftT '1 OF OPERATIONS
Data collection commenced at the northern end of the
suborbital track. Continuous flow measurements of
chlorophyll-a were not obtained due to fluorometer
failure; continuous radiometric sea surface tempera-
ture was recorded on a dual channel recorder. While
on the track, hourly XBT's, surface bucket tempera-
ture, and surface salinity were taken. Spectra of
upwelling and downwelling visible radiation and
measurements of scattering ratios were not observed
due to rough seas. Loran A fixes were made at one
hour intervals and at major course, and/or speed
changes.
Easterly winds in excess of 30 knots blew during the
entire survey. In the current the seas were 4-6
meters. On the night of 12 January, gusts in excess
of 50 .knots were encountered; all scientific opera-
tions were secured and the captain, with the con-
currence of the chief scientist, turned for sheltered
waters. A second XBT section was obtained on the
return leg. The following week, under calmer weather
conditions a deep sea tide gauge was retrieved by
H. Mofjeld. He obtained two additional crossings
which gave us a reasonably good view of the shape of
the Loop Current for the month.
VI. LOGS
Chief Scientist Log
Deck Log
Track Chart
Loran Log (C&GS 722)
Hydrographic Station Log
Bathythermograph Log
Submitted by: George A. Maul
January 21, 1973
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
ATLANTIC OCEANOGRAPHIC AND METEOROLOGICAL LABORATORY
PHYSICAL OCEANOGRAPHY LABORATORY
NASA/GSFC
CRUISE REPORT
R/V VIRGINIA KEY
13-19 February 1973
I. OBJECTIVES
The purpose of this cruise was to continue a time series
*of the location of the Loop Current as part of AOML's
project with the Earth Resources Technology Satellite
(ERTS) and the NOAA-2 Meteorological Satellite. The
research is intended to obtain baseline information on
the spectroradiometric properties of the ocean's sur-
face useful for remote sensing and the detection of that
information at orbital altitudes.
II. ACTUAL SCHEDULE
Date Time Activity
February EST
13 1500 Depart Miami
14 0800 Arrive Key West; fuel
1500 Depart Key West
1700 Commenced XBT transect of Florida Strait.s
15 2145 Commence XBT transect of Yucatan Straits
16 0700 Commence tracking current
1000 Satellite Transit
18 1830 Complete Sruvey
19 1800 Arrive Miami-
I
-2-
III. STATION POSITIONS
The northern limit XBT transect of the Florida Straits
was at the 100-fathom curve south of Marquesa Key Light
and terminated 12 n. mi. north of Havana Cuba. The
station locations were:
24 21'N 82-14W Station 10
24011'N 82-16W 11
240 01'N 82-18W 12
230 51'N 82-21W 13
23 41'N 82-23W 14
230 31'N 82-26W 15
230 21'N 82-28W 16
The station locations for the Yucatan Straits XBT
transect were:
21 50'N 85 11'W Station 1
21 48'N 85 21'W 2
21 46'N 85 32'W 3
·21 44'N 85 42'W 4
21 42'N 85 53'W 5
21 40'N 86 O3'W 6
21 38'N 86 13'W 7
21 36'N 86 24'W 8
21 34'N 86 34'W 9
The easternmost station was 12 n. mi. west of Cabo San
Antonio; the westernmost station was 12 n. mi. east of
Isla Contoy.
The cruise from Isla Contoy to Dry Tortugas was a
saw-toothed path, which crossed the surface boundary
layer zone of the current.
IV. PERSONNEL-
G. Maul, Chief Scientist NOAA/AOML
M. Ednoff FSU
C. Thacker NOAA/AOML
-3-
V. DESCRIPTION OF OPERATIONS
Data collection commenced with a T-7 XBT transect of
the Florida Straits; the STD was non-operational.
Continuous flow measurements of chlorophyll-a and
continuous radiometric sea surface temperature were
recorded on a dual channel recorder. While on the
track, hourly XBT's, surface bucket temperature,
surface salinity, and measurements of scattering
ratios were taken. Spectra of upwelling and down-
welling visible radiation were not observed. Loran
A fixes were made at one hour intervals and at major
course, and/or speed changes. One liter samples were
filtered for a spectrophotometer calibration of
chlorophyll-a every six hours and at major changes in'
the fluorescence, and for biological samples.
With the change in vessels to the VIRGINIA KEY, the
cruise plan was revised. This saved 300 n. mi. over
the old plan which was developed for a home port of
St. Petersburg. The suborbital track is considerably
shortened with the plan to occupy about 50 miles of
it each trip, as part of the current tracking routine.
VI. LOGS
Chief Scientist Log
Deck Log
Track Chart
Loran Log. (C&GS 722)
Hydrographic Station Log
Bathythermograph Log
Submitted by: George A. Maul
February 25, 1973


The author has identified the following significant results. Monthly field experiments in support of the NOAA investigation of ocean color boundary determination using ERTS-1 data have been conducted since June 1972. The boundary between coastal waters and the Loop Current has been detected by ERTS-1 as a result of sea state changes as well as color differences. Ocean information is contained in all 24 channels of the Bendix MSS flown on the C-130 in June 1972; this includes UV, visible, reflected IR, and emitted IR. Computer enhancement of MSS data is revealing many features not shown in the NDPF product

The author has identified the following significant results. A time series of the Loop Current in the Gulf of Mexico, covering an annual cycle of growth, spreading, and decay, has been obtained in synchronization with ERTS-1. Computer enhanced images, which are necessary to extract useful oceanic information, show that the current can be observed either by color or sea state effects associated with the cyclonic boundary. The color effect relates to the spectral variations in the optical properties of the water and its suspended particles, and is studied by radiative transfer theory. Significant oceanic parameters identified are: the probability of forward scattering, and the ratio of scattering to total attenuation. Several spectra of upwelling diffuse light are computed as a function of the concentration of particles and yellow substance. These calculations compare favorably with experimental measurements and show that the ratio of channels method gives ambiguous interpretative results. These results are used to discuss features in images where surface measurements were obtained and are extended to tentative explanation in others

The author has identified the following significant results. Sea ice is detectable in all of the MSS bands and can be distinguished from clouds through a number of interpretive keys. Overall, MSS-4 and 5 appear to be better for mapping the ice edge, whereas MSS-7 provides greater detail in the ice features

Remote sensing of ocean currents using ERTS imagery

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